Thanks for your answer @modemlooper
I tried this but didn’t succeed yet :
I enabled WordPress Network on site1 :
Site 1 configs are :
WordPress address (URL) for the site1 is : http://mydomain.com/site1
And the site adress (URL) : http://mydomain.com
I added site2 to « my sites »
I can enable Buddypress on network but with the template of site1 (the main site) not site2
Is there a way to enable Buddypress on network from site2 ?